The excellent mechanical and chemical properties of vinyl chloride homopolymers and copolymers and the versatility of such polymers to compounding variations has resulted in their widespread commercial use for fabricating various structural components, decorative fabrics and films, electrical wiring, floor coverings and the like. The high level of chlorine in vinyl chloride polymers (57%) and vinylidene chloride polymers (73%) renders these resins flame resistant and self-extinguishing in a rigid non-plasticized condition. However, many commercial applications necessitate the inclusion of substantial quantities of plasticizers in such resin formulations to provide the required degree of flexibility consistent with the intended end use. The inclusion of appreciable quantities, such as from about 20 phr up to about 100 phr of ester-type plasticizers, significantly reduces the flame resistant and self-extinguishing characteristics of such vinyl chloride polymers. The inclusion of such flammable ester-type plasticizers is also accompanied by an increased tendency of such plasticized formulations to generate smoke when exposed to elevated pyrolysis temperatures during fires which in many instances create a source of danger to imperilled personnel which is greater than the fire itself. In recognition of the reduced flame retardancy characteristics of such ester-type plasticized vinyl chloride polymers, secondary plasticizers possessing flame retardancy characteristics, such as chlorinated paraffins and organic phosphate esters, have been incorporated as a substitute for a portion of the ester-type plasticizer. While an improvement in the fire retardancy characteristics is usually achieved, the magnitude of flame retardancy attained is inadequate in many instances, and the smoke generation characteristics of such inhibited formulations are still objectionable.
Significant improvements in the flame resistance of such plasticized vinyl chloride polymers have been achieved by incorporating effective amounts of antimony oxide but without any significant reduction in the smoke generation characteristics of such resin compositions. A variety of other organic and inorganic compounds and salts have heretofore been proposed or used to increase the flame retardancy characteristics of such plasticized vinyl chloride polymers or to reduce the smoke generation characteristics thereof, but such agents have been universally deficient in providing an optimum improvement in both of these critical properties. Some of the agents heretofore employed are toxic themselves, or form volatile toxic compounds during combustion, further aggravating the hazard associated during a fire involving articles containing such polymers. The unpredictable behavior of various additive agents on the flame resistance and smoke generation properties of plasticized polyvinyl chloride resins has heretofore resulted in resin formulations possessed of less than optimum flame retardant and smoke suppression properties.
The present invention overcomes many of the problems and disadvantages associated with plasticized vinyl chloride polymers by providing a resin formulation including effective amounts of a material which functions both as a flame retardant agent and a smoke suppressant agent, which is of comparatively low toxicity, which is not itself volatilized when heated to an elevated pyrolysis temperature, but instead remains in the char; which is more economical than many other agents heretofore employed on a cost-effectiveness basis; which is available in good supply from domestic sources; and which is of versatile use in compounding vinyl chloride polymeric compositions.